Abstract
After frying pieces of sweet potatoes and onions five times at intervals of a week with the commercial soybean oil, TBA, carbonyl, acid and peroxide values of the oils were measuredand also these were compared with those of fresh oil.
Any of these values did not vary linearly, but now decreased and then increased. Accordingto the above results, these testing method seemed not to be appropriate to know the gradeof rancidity of oils which were heated on cooking.
